Tunable optical delay using photonic crystal heterostructure nanocavities

We demonstrate tunable optical delay in a coupled resonator structure consisting of a chain of three heterostructure nanocavities. The group index of the device is measured using an interferometric technique, and the tuning is accomplished by the use of an optical pump that selectively heats one of the cavities in the array, altering the coupling and so changing the delay of the system. The speed of light in the device is varied over a range from $c∕75$ to $c∕120$ using effective pump powers below $100\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{W}$.